1. Field of the Invention
The invention relates to deflecting devices in sorting machines for sorting essentially flat objects such as letters. More particularly, the invention is directed at a deflecting device for guiding letters into one of a plurality of selectable directions as input to, for example, a buffer system for the purpose of electronically sorting letters provided with a sorting code.
2. Prior Art
Such a deflecting device with a buffer system adjoining it and containing a number of buffer positions for the temporary storage of individual letters for the purpose of a sorting process is known from reference [1] mentioned below under C. A single endless conveyor forming a main conveyor track runs over the entire length at the input side of said buffer system. Each buffer position in the buffer system is formed by two interacting endless conveyor belts, one of which, upstream of the input to the buffer position, interacts in each case, while also running parallel over a certain length, with the endless conveyor for the purpose of conveyance in the on-going main conveyance direction. Situated opposite each buffer input on the other side of the conveyor, and therefore pointing downstream, are deflecting means with which it is possible, on command (of a control signal originating from a control device), to intervene in the main conveyor track in order to route a particular letter to the buffer position corresponding to the deflecting means. The deflecting means suggested by this known technique are those of the roller type which, at the position of the endless conveyor, push in the direction of the buffer input. However, this known technique has the following drawbacks. The chosen sorting process is such that all the stored letters must be able to leave the buffer system simultaneously via an outgoing conveyor track running parallel to the input conveyor track. This implies that the width of each buffer position, that is to say, also the distance between two consecutive input deflecting positions, must at least be larger than the maximum length of letter permissible for the system. For a large number of buffer positions, necessary for a flexible buffer sorting process, this condition requires an unacceptably high space occupancy. Although this minimum width will be capable of reduction if the principle of simultaneous ejection is abandoned, the chosen manner of conveyance along the main conveyance direction does not permit any appreciable reduction. In addition, in the case of on-going conveyance in the main direction, a direction deviating from the latter and not selected is not screened off, as a result of which conveyance in an unintended direction is not excluded under some circumstances.
Such a deflecting device in which, in the event of on-going conveyance in the main direction, each selectable direction deviating therefrom and not chosen is, however, in fact screened is known from reference [2]. The screening is done with the aid of what is described as a trap, which has a V-shaped cross section and is rotatable at the root. In the closed state, the traps form an essentially continuous sliding surface with a first side wall. Arranged opposite each of said first side walls is a deflecting roller. A driven endless conveyor belt extends between the successive first side walls of the traps and the successive deflecting rollers in a manner such that letters clamped between conveyor belt and the continuous sliding surface can be conveyed in a sliding/entraining conveyor in the main direction. The other side wall of every trap, also provided with a sliding surface, forms a sliding wall of the directly preceding selectable direction in :he closed state. For the deviation of a letter in a particular selectable direction, the appropriate trap is opened by turning it away from the conveyor belt. At the same time, the associated deflecting roller is turned in the direction of the opening formed under these circumstances, the conveyor belt at this point being deflected from the main direction and, as a consequence, being able to convey an approaching letter in the desired selectable direction. This known deflecting device has the following disadvantages. Although every selectable direction not chosen in the event of on-going conveyance in the main direction is well screened, in the event of deviation in a selectable direction leading away from the main direction, the on-going direction is, on the contrary, not well screened as a consequence of the use of roller-type deflecting means. Flexible letters which continue to stick to the conveyor belt, for example, as a consequence of static electricity, will not, or will only poorly, be deflected. To execute the deflecting function, the deflecting roller has to force the belt aside, and this makes a relatively large energisation necessary, permits only a limited deviation angle and, in addition, operates sluggishly and inaccurately. During deviation from the main direction to a selectable direction, there is no clamping in situ and therefore no well-defined conveyance of the letter.
Another such deflecting device used in a buffer system having a number of buffer positions for the temporary storage of individual letters for the purpose of a sorting or a video coding process is known from reference [2] mentioned under C. This known deflecting device comprises, for each buffer position, a deflecting tongue which, in the quiescent state, completely closes off the access to the buffer position like a door. The buffer positions form a row of buffer positions which adjoin a common main conveyor track, as it were, like `scales` at an angle of approximately 30.degree.. Said main conveyor track is formed by an endless conveyor which can interact in a sliding/entraining conveyor system with sliding means mounted on an outside of the deflecting tongue. In the activated state, the deflecting tongue intervenes as a pointing-upstream deflector in the conveyance along the main conveyor track and causes a letter approaching therein to deviate in the direction of the buffer position by means of its front. Although this known deflecting device makes a very compact buffer system possible, it is under certain circumstances fairly susceptible to malfunction as a result of using a deflecting device of the pointing-upstream deflector type. Conveyance based on the sliding/entraining principle also imposes very high requirements on the wear resistance of the materials used.